Electrically heatable cylindrical sample container

ABSTRACT

AN ELECTRICALLY HEATABLE CYLINDRICAL SAMPLE CONTAINER MADE OF A GRAPHITE OR CARBON MATERIAL IS DESIGNED AS A CLOSED CAPSULE. THE DEVICE IS USE FOR TESTING SAMPLES, PARTICULARLY FOR THE ANALYTICAL DETERMINATION OF THE GAS CONTENT OF THE SAMPLE AND IT IS ADAPTED TO BE CLAMPED BY ITS UPPER AND LOWER ENDS BETWEEN TWO CURRENT SUPPLY ELECTRODES IN A VACUUM FURNACE AND BE HEATED IN THE FURNACE BY THE DIRECT PASSAGES OF CURRENT THERETHROUGH. THE CONTAINER IS MADE OF A BARREL-LIKE OR CYLINDRICAL CONFIGURATION AND A ZONE OF THE CONTAINER WHICH ATTAINS THE HIGHEST TEMPERATURE WHEN IN A VERTICAL POSITION OF USE IS DESIGNED SO THAT THE BOTTOM FACE OF THE INTERIOR OF THE CONTAINER WILL BE LOCATED AT A LEVEL SO THAT IT IS EMBRACED BY THE HIGHEST TEMPERATURE ZONE DURING OPERATION. FOR THIS PURPOSE THE CONTAINER MAY BE DESIGNED AS A TUBULAR OR BARREL-LIKE MEMBER HAVING A RECESSED BOTTOM WALL SO THAT THIS WALL WHICH CONTAINS THE MATERIAL BEING TESTED WILL BE LOCATED TOWARD THE HOTTEST FURNANCE ZONE. A FURTHER POSSIBILITY FOR SHIFTING THE HOTTEST FURNACE ZONE TOWARD THE LOWER END OF THE CONTAINER IN ORDER TO INTENSIFY THE GENERATION OF HEAT AT THIS LOWER END IS TO PROVIDE A TAPERING OF THE LOWER END OF THE CONTAINER..

ELEUTRICALLY'HEATABLE CYLINDRICAL SAMPLE CONTAINI'J'R Filed Feb. 4. 1970 IO 8 '6 a 2| l (PnorArt) (Prior Art) FIG 2 FIG.I

3s I 32 N! 3 INVENTORS THADD'AUS KRAUS GEROLD PAESOLD 5mm METZLER ATTORNEYS United States Patent ELECTRICALLY HEATABLE CYLINDRICAL SAMPLE CONTAINER Thaddiius Kraus, Vaduz, and Gerold Paesold, Balzers, Liechtenstein, and Elmar Metzler, Feldkirch, Austria, assignors to Balzers Patent- Und Beteiligungs-AG, Balzers, Furstentum, Liechtenstein Filed Feb. 4, 1970, Ser. No. 8,521 Int. Cl. F2711 11/02 US. C]. 13-20 6 Claims ABSTRACT OF THE DISCLOSURE An electrically heatable cylindrical sample container made of a graphite or carbon material is designed as a closed capsule. The device is used for testing samples, particularly for the analytical determination of the gas content of the sample and it is adapted to be clamped by its upper and lower ends between twocurrent supply electrodes in a vacuum furnace and be heated in the furnace by the direct passage of current therethrough. The container is made of a barrel-like or cylindrical configuration and a zone of the container which attains the highest temperature when in a vertical position of use is designed so that the bottom face of the interior of the container will be located at a level so that it is embraced by the highest temperature zone during operation. For this purpose the container may be designed as a tubular or barrel-like member having a recessed bottom wall so that this wall which contains the material being tested will be located toward the hottest furnace zone. A further possibility for shifting the hottest furnace zone toward the lower end of the container in order to intensify the generation of heat at this lower end is to provide a tapering of the lower end of the container.

SUMMARY OF THE INVENTION This invention relates in general to the construction of an electrically heatable container for samples of material which are to be analysed as to gas content and in particular to a new and useful container constructed so as to provide a high temperature zone which is located at the bottom wall which is adapted to contain sample material.

The present invention is applicable for the testing of substance samples particularly for the purpose of the analytical determination of their gas content. A method is known- Whereby the samples to be tested is enclosed in a small container of graphite or carbon which is gripped between two electrodes in a vacuum furnace and heated by the direct passage of current through the container. The gases which are given olf by the sample, will issue from the container and they are collected and fed to a measuring device for the determination of their type and quantity. For the extraction of a sample, the sample is heated to a temperature of about 3000 degrees centigrade when it is in its container which is clamped between current-supply electrodes which are supplied with direct current which is passed through the sample container. The quantity of heat evolved during the short heating time is absorbed by the metal mass of the elecr trodes and is carried away to the outside during the intermission until the nextsample is heated. The electrodes can be cooled by passing a coolant therethrough. The gases which evolve during the heating are pumped away from the interior of the device to gas analyzers.

By exact studies it was found that with sample capsules which are normally used, that there is a likelihood that there would be an error due to the inevitable acci- 3,619,839 Patented Nov. 16, 1971 dental fluctuation of the emptied value of the container. Little is known about the causes of this error but it is logical to attribute it to irregular degasing. On the basis of this reasoning it is essential to provide for as uniform as possible a temperature distribution in the sample container in order to ensure uniform degasing. At the present time, containers are known which provide for the damming of the heat flow at the gripping ends of the container in order to provide a more uniform temperature distribution at the interior. The damming of the heat flow is achieved by notches at the gripping ends of the container which narrows the conductor cross section at the expense of mechanical strength.

Studies by the inventors of the present case have shown that with such a sample container the sample melt has an irregular distribution within the container space and this probably contributes to the heavy fluctuation. of the gas analysis results. In fact, after solidification, the melt usually remains on one side of the container wall and is lifted oif the container bottom. In some instances it forms on the inner wall in the form of a closed ring which extends around the bottom. Such an irregular distribution which varies from case to case must be the reason for the heating of the individual wall portions at different rates and hence the varying of the evolution of the gas. This is especially true when electrically conducting samples :are employed so that sections of different values of resistance of the heated container barrel are short circuited electrically. Thus, the local power input, the generation of heat, and hence the temperature distribution in the sample container is influenced in an uncontrolled manner.

In accordance with the present invention, there is provided a container which provides reliable operations for the evolution of the gas from the material for analysis purposes, and which will operate without the above mentioned disadvantages. The container of the invention comprises an electrically heatable cylindrical sample container preferably of a graphite or carbon material which is designed as a closed capsule. The containers are adapted to be gripped by its lower and upper ends between two current supply electrodes in a vacuum furnace and heated by the direct passage of current. The container is formed with a barrel zone which attains the highest temperature in the case of the vertical position of its use and it is characterized by a construction by which the bottom face of the interior of the container is located at a level sufficiently high that it is embraced by the barrel zone which in operation assumes the highest temperature. Thus, unlike the prior art arrangement, the high temperature zone is not located in the middle between the two container ends and the melt obtained after the melting down of the sample is present below the high temperature zone. With a container constructed in this manner, a substantial reduction of the scatter of the analysis results can be obtained.

Accordingly, it is an object of the invention to provide an improved container construction for holding samples of material between electrodes so that they may be heated to evolve the gas therefrom and which includes a cylindrical wall or barrel shaped wall portion having a bottom part which is located at a spaced location from the bottom end in a position to receive the melt material and hold it during operation in the hottest zone of the cylindrical barrel thus formed.

A further object of the invention is to provide a container for holding samples of material which are to be heated to evolve gas therefrom for analysis and which is rugged in design, simple in construction, and economical to manufacture.

The various features of novelty which characterize the invention are pointed out with particularity in the claims u annexed to and forming a part of this specification. For

a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a sectional view of a device for heating a sample container in order to evolve gases from the material being tested and constructed in accordance with the prior art;

FIG. 2 is a container used with the device of FIG. 1 and constructed in accordance with the prior art;

FIG. 3 is a sectional view through a container constructed in accordance with the invention; and

FIG. 4 is a view similar to FIG. 3 of another embodiment of the invention.

GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENTS A known furnace for heating of materials in a sample container 5 of known construction is indicated in FIG. 1. The device comprises a vacuum furnace which includes electrodes 1 and 2 which define a fluid-like recess or cavity 2 therebetween with a projection 1' extending into an enlarged recess portion of the electrode 2 and providing a means for clamping the sample container 5 therebetween. The container 5 is heated by current supplied through conductors 13 and 14. For the cooling of the container 5, the electrodes 1 and 2 form a two-part metallic body of certain heat capacity which closely embraces the container and which includes cavities 11 and 12 which are connected through conduits 7, 8, 9, and for the circulation of a cooling liquid into and out of these passages. The engaged electrodes 1 and 2 provide a shield against access of evaporated container material into the electrically insulated gap between the electrodes which is designed as an actuation channel.

When a sample material is placed in the container 5, it is heated to about 3000 degrees centigrade when it is clamped between the electrodes 1 and 2 and a direct cur rent is passed therethrough. The quantity of heat evolved during the short heating time is absorbed by the metal mass of the electrodes 1 and 2 and is carried away to the outside during the intermission between the testing of samples. The electrodes 1 and 2 can be cooled by passing a coolant through the cavities 11 and 12 via the pipelines 7 to 10.

The gases which are given off by the sample during the heating process diffuse through the wall of the container 5 and are pumped off in a path indicated by the arrows in FIG. 1 by a pump (not shown) which is connected through a suction conduit defined in a member 16. The gases which are removed are directed to a gas analyzer (not shown).

During evacuation the pressure for the application of the electrodes against this sample container 5 is produced automatically by the pressure of the external atmosphere but it may have to be reduced depending on the size of the electrode faces and upon the strength of the sample container. For this reason, a compression spring 9 is arranged around a rod 30 and bears in respective opposite directions against a nut 20 and a ring 32 of the upper housing. The upward force of the spring against the ring 32 to lift the housing upwardly may be adjusted by the position of the nuts 20. The force exerted on the container 5 in the closed state is thus reduced by the spring force of the spring 19.

Before an analysis is performed a so-called empty or blank value is determined, that is, the quantity of the test gas, for example, carbon monoxide (CO) or nitrogen (N which is given off during a period of time while the furnace is being heated with an inserted but empty sample container. This empty volume must be detected from the value of the gas quantity pumped off from the furnace measured when a sample is extracted in order that a true value of the test gas quantity of this sample be determined. The empty value of the furnace derives from the gas given off by the sample container, in particular water vapor, and it should be low as possible in order that the sample having only a little evolution of gas can be measured reliably.

When a known sample container of the type indicated 5' in FIG. 2 is used, the sample material is placed in a lower cylindrical receptacle part 21 which is closed by a cover 22. With such a container, the sample melt has an irregular distribution in space and this probably contributes to the heavy fluctuation of the analysis results. After solidification the melt 23 is usually on one side of the wall and it is lifted oif the contained bottom. Sometimes it forms on the inner wall in the form of a closed ring around the bottom. Such an irregular distribution varies from case to case and it gives rise to different heating of the individual wall portions and hence to a varying evolution of gas. This is especially true when electrically conducting samples are employed and they act to provide a short circuited flow path for the electric current heating element.

In the embodiment of the invention indicated in FIG. 3, there is provided a container generally designated 50 which has an exterior cylindrical or barrel shaped wall 34 and a bottom part 32 which is spaced upwardly from the lower end of the bottom edge defined by the exterior wall 34. A removable cover 33 includes a cylindrical outer part 35 forming a projecting cylindrical end which, together with the end 34, are adapted to be gripped between the electrodes of the furnace described in respect to FIG. 1. A cavity or recess therefore is formed at each end at 38 and 39 and they reduce the flow of heat.

In accordance with the invention the bottom face 32a of the interior of the container is so placed by proper dimensioning of the thickness and position of the Wall 32 that the melt 36 will remain during operation in the hottest zone of the cylindrical barrel 31. The location of the hottest zone can be calculated in the construction of the sample container or be determined by preliminary tests. Expediently, the bottom face 32a is placed so that it is at a level of the lower edge of the barrel zone which in operation assumes the highest temperature.

A variation of the inventive container construction is indicated in FIG. 4, wherein similar parts are similarly designated to that of FIG. 3 but with primes added. In this construction, the ends are formed so that they dam the heat flow more at the lower grip end 34' than at the upper grip end 35', so that the hottest zone of the furnace will be displaced closer to the lower end 34'. With such a construction, the space between the two gripping electrodes will be utilized better. In order to obtain the desired heat damming the projecting cylindrical barrel portion 34 at the bottom is designed so it is significantly longer than the cylindrical portion 35' at the top.

A further possibility of operation is to design the furnace indicated in FIG. 1 so that there is an intensity of the heating at the lower end of the Zone that is by the location of the electrode 2 and this is achieved by proper tapering of the electrical conductor cross section. Therefore, for this purpose, the cylindrical wall portion 34' at the lower end is provided with a taper inwardly toward this lower end.

As indicated in FIGS. 3 and 4, as the solidified material melts, there results, in the sample container constructed according to the invention, a reliable adhesion of the melt on the bottom surface 32a and 32a of the respective embodiments and this is without detachment. This means that the disadvantages of the prior art containers has been eliminated. Proceeding from a constant container filling one achieves in the routine testing of simple samples. as would occur for example in the continuous control of steel production and steel mills, a constant covering of the inner walls of the container with the melt and hence a constant heating and evolution of gas thereof. Presumably this is the reason for the smallest scatter of the test values when using sample containers according to the invention. The variation of the passage of current through the capsule is only about 10% as against more than 20% in sample capsules of the known kind.

What is claimed is:

1. An electrically heatable cylindrical sample container of a material such as graphite or carbon and which is designed as a closed capsule for testing of samples particularly for the analytical determination of the gas content, comprising a container of graphite material utilized as a resistor heater and having a cylindrical wall having a bottom closing one end defining an interior surface adapted to receive the sample material, a cover closing the opposite end of said container, said cover and the portion of said container below said bottom being adapted to be gripped between two current supply electrodes in a vacuum furnace and heated by the direct passage of current therethrough, the interior of said bottom defining a receiving face for the sample material which will be located at a level spaced upwardly from the lower end of said cylindrical wall by an amount suflicient to locate it in the highest temperature Zone during operation.

2. A container, according to claim 1, wherein said interior bottom face is present at the level of the lower edge of the barrel zone which assumes the highest temperature in operation.

3. A container, according to claim 1, wherein said cover has an upper end and said cylindrical wall has a lower end which are formed of a thickness and length to provide for a greater damming of the heat flow at the lower end than the upper end.

4. A container, according to claim 1, wherein said cover and said container each includes cylindrical outer wall said cover and said container having an end recess therein.

5. A container, according to claim 1, wherein said bottom is spaced upwardly from the lower end of said cylindrical wall, said cover having a cylindrical wall extending upwardly from a cover closing portion and defining a recess, the recess defined between said bottom and the lower end of said cylindrical walls being greater at the bottom than at said cover.

6. A container, according to claim 1, wherein said container cylindrical walls taper at the lower ends said bottom being recessed upwardly from the lower ends of said outer container cylindrical walls.

References Cited UNITED STATES PATENTS 1,743,035 1/1930 Halvorson 23-230 PC UX 2,930,602 3/1960 Rohn 23-253 PC UX 2,964,389 12/1960 Bennett et al. 23-253 PC 3,372,993 3/1968 Brown 23-230 PC UX BERNARD A. GILHEANY, Primary Examiner R. N. ENVALL, J 11., Assistant Examiner US. Cl. X.R. 23-230 PC; 263-48 

